1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device with high reliability, and, more particularly, to a method of manufacturing a semiconductor device which includes a wiring layer having satisfactory contact characteristics.
2. Description of the Related Art
In recent years, in order to achieve high integration of integrated circuits, wiring layers have been miniaturized and more layers have been formed in the integrated circuits. In a semiconductor device having the above structure, an increase in the wiring capacitance problematically occurs. Such an increase in the wiring capacitance causes an increase in signal delay between wiring layers.
In one method for reducing the wiring capacitance, a material having low relative permittivity is employed as an interlayer insulating film. An organic insulating film which is formed of a BCB (Benzocyclobutene) resin serves as an insulating film having low permittivity. A BCB film is formed of a resin in which a precursor monomer having the structure illustrated in FIG. 4 is polymerized. The relative permittivity of the BCB film is approximately 2.8 which is quite low.
In the case where a contact hole is formed in the interlayer insulating film which is formed of an organic insulating film such as a BCB film, etc., it is necessary to form a minute opening in a thick interlayer insulating film with high accuracy. Thus, an etching technique, for etching the organic film without forming tapered side wall in the contact hole, is needed for etching the organic film with high anisotropy.
Such an etching method is disclosed, for example, in Unexamined Japanese Patent Application KOKAI Publication No. H2-244625. In this etching method, a mixture of Cl2/O2 is employed as an etching gas, and an organic insulating film (resist film) is anisotropically etched using an RIE (Reactive Ion Etching) technique while using an SOG (Spin On Glass) film as a mask.
Another etching method for etching an organic film, especially the BCB film, is the one disclosed in M. Schier, J. Electrochem. Soc., Vol. 142, No. 9, September 1995 (pp. 3238-3240). In this method, a mixture of CF4/O2 or SF6/O2 is used as an etching gas, and the BCB film is anisotropically etched using an RIE technique with a SiN or SiO2 film as a mask. A method for etching the BCB film using a mixture of CF4/O2 or a mixture of SF6/O2 is disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H8-181087.
In the case where an organic insulating film is etched using a mixture of Cl2/O2, an etching selective ratio (ratio of etching rates) of an SOG film (for example, SiO2) to a resist film is sufficiently large. However, in the case where a BCB film is used in place of a resist film, an etching selective ratio of an organic insulating film to the BCB film is small. Therefore, the etching of the BCB film under high anisotropy can not satisfactorily be achieved, because the width of an opening get broadened during an etching process.
In the case where the BCB film is etched using a mixture of CF4/O2 or a mixture of SF6/O2, an etching selective ratio of a SiN film serving as an etching mask to the BCB film is not big enough, thus the processing accuracy of the etching is low.
By increasing the percentage of O2 in the etching gas, the etching selective ratio of the BCB film to the mask can be increased. However, the increase in the percentage of O2 within the etching gas brings a disadvantage that the side wall of a contact hole which is formed during the etching gets roughened.
The low anisotropy or low processing accuracy in the etching of the organic insulating film, such as a BCB film, etc., lowers the contact characteristics of a wiring layer to be formed. This results in low reliability of a semiconductor device including an organic insulating film.
It is accordingly an object of the present invention to provide a method of manufacturing a semiconductor device with high reliability, and, more particularly, to a method of manufacturing a semiconductor device including a wiring layer which has preferable contact characteristics.
Another object thereof is to provide a method of manufacturing a semiconductor device including a BCB film having a contact hole obtained by etching the BCB film under high anisotropy.
In order to achieve the objects, there is provided a method of manufacturing a semiconductor device, comprising:
forming an organic insulating film on a substrate;
forming a mask on the organic insulating film; and
etching the organic insulating film through the mask so as to form a hole, using an etching gas including Cl2, BCl3 and O2.